Sexually Transmitted Diseases (STDs): Condition Information

What are STDs and sexually transmitted infections(STIs)?

STDs are a group of illnesses that are passed from person to person during sexual intercourse, oral sex, or sex play. These diseases can be caused by bacteria, viruses, yeasts, or parasites and are spread through intimate sexual contact involving the penis, vagina, mouth, or anus. STDs are also called venereal diseases or STIs. Health care professionals prefer the term "infection" rather than "disease," because it is possible for a person to have no symptoms but still carry the bacterium or virus and require treatment. Scientists have identified more than 20 different STDs/STIs.1